QHostInfo: simplify assignment operator

The d_ptr is never nullptr. If it could be, then other's d_ptr could
also be nullptr, and we would dereference the null pointer.

Guarding against self-assignment is nevertheless a good practice.

Fixes static analyzer warning
5fc3780532e30c6350a0aa1ad2188a4c.

Pick-to: 6.1
Change-Id: I07ff808e4c4f5bf07b4d6663f1fb4a3301a0fec7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/network/kernel/qhostinfo.cpp

@@ -609,10 +609,11 @@ QHostInfo::QHostInfo(const QHostInfo &other)
 */
 QHostInfo &QHostInfo::operator=(const QHostInfo &other)
 {
-    if (d_ptr)
-        *d_ptr = *other.d_ptr;
-    else
-        d_ptr = new QHostInfoPrivate(*other.d_ptr);
+    if (this == &other)
+      return *this;
+
+    Q_ASSERT(d_ptr && other.d_ptr);
+    *d_ptr = *other.d_ptr;
     return *this;
 }